A Terraform module can become hard to navigate even when it works correctly. Internal refactoring changes its structure to make future work easier without changing its external behavior or interface. A test suite provides a safety net: if an internal change breaks tests, investigate for unintended consequences. section 9.5.1 section 9.5.2
A module’s input variables and outputs form its external interface. Changing an existing input or output is an external change that users may notice; reorganizing code without changing either is most likely internal. This distinction matters because breaking changes need more careful management. section 9.5.2 section 9.7
For a straightforward reorganization:
- Keep inputs in variables.tf and outputs in outputs.tf; group related declarations with clear headers. section 9.5.3
- When main.tf grows unwieldy, use headers or split resources into files by function, such as networking, load balancing, and logging. Apply the same convention across modules. section 9.5.3
- Check the plan. Terraform’s dependency graph does not depend on resource order or which file contains a resource, so a file-only move should produce no planned changes. section 9.5.3
Listing 9.32 Variable file with group headers
#########################
# Networking
#########################
variable "vpc_id" {
type = string
description = "The ID of the VPC to deploy the resources into."
}
variable "subnet_ids" {
type = list(string)
description = "A list of subnet IDs to deploy the resources into."
}
#########################
# Load Balancing
#########################
variable "acm_certificate_arn" {
type = string
description = "The ARN of the ACM certificate to use for the
load balancer."
}
#########################
# Logging
#########################
variable "cloudwatch_log_group_name" {
type = string
description = "The name of the CloudWatch log group to send logs to."
}
Grouped variable declarations show how to improve navigation while retaining the same inputs. section 9.5.3
Moving code between files is different from changing a resource’s address by renaming its block or moving it into a module. For an address change, a Terraform moved block associates the existing resource with its new location without re-creating it. Refactor regularly to limit technical debt, but keep interface changes separate from work intended to be invisible to users. section 2.9 section 9.5.1
